This allows you to use the 4-48 (English) contact points with your (Metric) threaded M2.5 Linear Gauge Sensors.
The male end will screw into the indicator spindle. The contact point will screw into the female end of the converter. The converter will add about 3/8" of length to your point.

M2.5 male to 4-48 female thread Converter

Thread Size

M2.5

The purpose of the AA-847 and AA-848 adapters are so that you may use either (metric) M2.5 or (english) 4-48 threaded contact points.